1. Field of Invention
The present invention relates generally to the field of wireless communication and data networks. More particularly, in one exemplary aspect, the present invention is directed to the implementation of a femtocell radio frequency setup procedure so as to minimize interference between other femtocells and/or base stations of the primary network operator.
2. Description of Related Technology
The deployment of additional base stations in a wireless network is a considerable capital expenditure for network operators. One proposed method of defraying the cost to a service provider is via user-initiated deployment of small cellular base stations, which are commonly referred to as “femtocells”. The intended mode of operation for a femtocell is to augment the service provider's existing network of base stations by connecting to the service provider's network via a broadband interface (such as DSL or cable). Due to the smaller size and cost of a femtocell, they can be distributed in areas which are otherwise not feasibly serviced through standard base station deployment (e.g., by extension of indoor service coverage, or temporary service coverage).
Femtocells are far cheaper to manufacture than a typical base station, and possess simpler software. Femtocells are also typically not fully featured, and cannot support the same number of users as a typical base station. Furthermore, femtocells offer complete and self-contained deployment. The relative cost and simplicity of operation allows a non-technical audience (i.e., residential and small business users) to purchase and operate femtocells. The benefits of femtocell deployment are shared between the user and the network. For a user, as mentioned above, the femtocell offers an inexpensive and easy method to selectively augment network coverage. Another distinct advantage of femtocells over other user managed ad hoc networks is their seamless integration with current network base stations, as opposed to the expensive hardware and software costs necessary for multi-mode capable transceivers.
Universal Mobile Telecommunications System (UMTS) and Femtocells—
The Universal Mobile Telecommunications System (UMTS) is an exemplary implementation of a “third-generation” or “3G” cellular telephone technology. The UMTS standard is specified by a collaborative body referred to as the 3rd Generation Partnership Project (3GPP). The 3GPP has adopted UMTS as a 3G cellular radio system targeted for inter alia European markets, in response to requirements set forth by the International Telecommunications Union (ITU). The ITU standardizes and regulates international radio and telecommunications. Enhancements to UMTS will support future evolution to fourth generation (4G) technology.
Currently, the standardization body for mobile communication (3GPP) is specifying a new network femtocell element called a “Home Node B” (HNB). This is a modified Node B (aka, UMTS base station) designed for use in buildings, with focus on home or residential environments, in order to increase in-building coverage. For example, in one exemplary usage case, a user of a mobile phone might wish to augment their wireless coverage by implementing a HNB in their apartment. The user employs a DSL connection to connect the HNB to the operator's Core Network. The usage is beneficial for both operator and user; i.e., the user may save money, improve data throughput, and conserve battery power for his mobile phone (by improved in-house coverage) when using his HNB. The operator gets additional network coverage area; see, e.g., 3GPP TR 25.820, “3G Home Node B Study Item Technical Report” v100 (Release 8), which is incorporated herein by reference in its entirety.
Flexibility of use is one important requirement for HNB operation. An HNB should be easy to use, and easily transportable, so that it can be used nomadically; e.g., the user may operate it one day in his apartment, and the next day on a business trip in a hotel. Additionally the HNB may be switched on and off unpredictably; an example of such erratic usage would be a user who does not operate the HNB at night while he/she is asleep.
The simplicity of HNB operation, and convenience of setup for the home user, also creates some unique challenges for network operators. Prior to the deployment of femtocells, base station networks were planned and deployed by a network operator, and were relatively static in nature. Physical network resources were also planned in advance by the base station operator. Network access functions such as security and authorization were easily controlled by a network operator through the base station fixtures as well. The nomadic usage of HNBs has significantly complicated these fixed base station network operations.
One such example of increased network complexity is the allocation of spectrum resources. Spectrum allocation is a major implementation issue for carrier networks. A typical Node B installation is running permanently at a fixed location. Based on its fixed geography, the operator allocates different radio resources (i.e., carrier frequencies or codes) to neighboring Node Bs. The neighboring Node Bs' geographic locations and distances are fixed; therefore radio frequency (RF) interference is minimized. Careful network planning is necessary, otherwise different UEs (User Equipment) connected to neighboring Node Bs may mutually interfere, and valuable spectrum resources inefficiently utilized, thereby imposing costs on the operators of these networks.
Several solutions have been contemplated in the prior art to address the issue of network radio frequency spectrum allocation including frequency detection, spectrum occupation (also referred to as free or usable), and spectrum selection. For example, U.S. Pat. No. 5,963,848 to D'Avello issued Oct. 5, 1999 and entitled “Method and apparatus for assigning a channel to a mobile unit in a wireless communication system” discloses a method and apparatus which determines which channels in a wireless communication system are both authorized for cordless operation and available. A channel is then selectively chosen from this list to reduce the probability that an interferer will be on the chosen channel. For example, the channel could be randomly selected from all available channels or randomly selected from a limited group of available channels to avoid co-channel interference. Alternatively, the channel could be chosen based upon the level of the signal that last caused that channel to be blocked. Finally, the channel could be chosen based upon the number of channels from an available channel to the nearest blocked channel.
United States Publication No. 20040235428 to Nagai et al. published Nov. 25, 2004 and entitled “Communication system, and endpoint device and interrogator” discloses a communication system wherein each endpoint device which has received an interrogating signal from an interrogator responds with a reflected signal generated by modulating the interrogating signal with appropriate information. Each endpoint device includes a distance detecting portion operable to detect a distance between the interrogator and the endpoint device; a reflecting portion operable to receive and reflect the interrogating signal; an information generating portion operable to generate replying information to be transmitted to the interrogator; a band determining portion operable to determine on the basis of the detected distance a frequency band of a modulating signal used to modulate a reflected signal generated by the reflecting portion; and a modulating-signal generating portion operable, according to the replying information, to generate the modulating signal having a frequency within the determined frequency band. The distance detecting portion may be provided in the interrogator, rather than in the endpoint device. The frequency of the modulating signal may be determined on the basis of the number of the endpoint devices ready for communication with the interrogator, or a distribution of overall frequency utilization ratio of the reflected signals received from the individual endpoint devices.
United States Patent Publication No. 20060294573 to Rogers et al. published Dec. 28, 2006 and entitled “Media distribution system” discloses a system, apparatus, method and article to distribute media information. The apparatus may include a transceiver to receive digital information representing media information. The apparatus may further include a processor to couple to the transceiver, the processor to select a modulation technique based on a receiver type and an ultra-high frequency channel using a cognitive algorithm. The transceiver may transmit the media information over the channel using the modulation technique.
German Publication No. DE4104890 to Dipling published Aug. 27, 1992 and entitled “Mobile radio telephone system—with disconnection of each battery-operated mobile station in traffic-free situation” discloses a radio telephone system that has each mobile frequency multiplex station coupled via a number of duplex speech channels with fixed stations, coupled to the telephone line network. The mobile stations exhibiting no communication traffic are cyclically disconnected and are switched back in via a time slot radio information signal transmitted by a fixed station and containing the addresses of each mobile station identified by the incoming traffic within the time slot. A quitting signal is provided for detecting the highest reception field strength to select the transmission path.
WIPO Publication No. 2003096590 to Logvinov et al. published Nov. 20, 2003 and entitled “Method and System of Channel Analysis and Carrier Selection in OFDM and Multi-Carrier Systems” discloses a method to channel estimation in OFDM systems. The embodiment of this invention is a block of new logic (16) and modifications performed to other components of the system, added to any existing OFDM receiver, which utilizes information available from other blocks as found in the receiver. This logic (16) would improve the units' error rate because of the improved channel quality estimations it makes available. This improvement is made possible because both channel noise data and channel signal data (11) are used in the estimation process. This data goes through a learning process over time and multiple data blocks for further improvements in the quality of the estimate. This improvement is possible without any direct communications with other remote units, but it could be used in a multi-node environment to improve the performance of the system as the whole.
WIPO Publication No. WO/2007/093653 published Aug. 23, 2007 to Herraiz et al., and entitled “Method and system for establishing a direct radio communication between two or more user devices in a cellular mobile communication system” discloses a method for establishing a direct radio communication between two or more user devices in a cellular mobile communication system, whereby said users are subscribed to the same operator. According to the invention, a cognitive radio technique is used to detect spectrum resources available for radio communications in a predetermined area containing said at least two user devices. The method is characterized in that it also includes the following steps in which: at least one resource is selected from the available resources, said resource being a resource of the operator common to the two or more user devices; and a direct radio link is established between said two users using the detected free resource of the operator. The invention also relates to a system for establishing a direct radio communication between two or more user devices in a cellular mobile communication system.
European Publication No. EP1248477 to Zimmerman et al. published Oct. 9, 2002 and entitled “Method and device for controlling dynamic frequency selection within a wireless communication system” discloses a method of controlling frequency selection within a wireless communication system in response to radar-like interference signals which comprises continuously or quasi-continuously monitoring and assessing one or more frequencies with respect to radar-like interference signals, allocating a quality parameter to each assessed frequency, the quality parameter indicating a probability that a frequency is occupied, and selecting one or more transmission frequencies in dependence on the allocated quality parameters. Optionally, a further monitoring of one or more frequencies with respect to at least one of the radar-like interference signals and other interference signals can be performed.
WIPO Publication No. WO2007040453 published Apr. 12, 2007 entitled “Automatic Configuration Of Pico Radio Base Station” discloses methods and apparatus to configure a femto radio base station. A macro receiver of the femto radio base station is used to acquire detected coverage information of a radio access network. The detected coverage information is used to determine an operation parameter for use by the macro transceiver of the femto radio base station. In one embodiment, the detected coverage information is transmitted to a control node of the radio access network. The control node determines the operation parameter and communicates the operation parameter to the femto radio base station. The femto radio base station is accordingly configured using the operation parameter for further operation towards UEs accessing the femto radio base station.
Other spectrum allocation schemes also exist in the prior art. For example, in the context of a wireless LAN (WLAN), WLAN Access Points scan the spectrum for electromagnetic interference and select a portion of spectrum with the lowest interference for transmission. The access point independently decides what the optimal spectral usage is, based on the used spectrum. A comparable solution is used in base stations for cordless telephones (e.g., DECT).
In addition to the above-described limitations of the prior art, standard UE operation cell selection procedures rely on the UE scanning for, and finding the strongest cell. The cell selection is performed by the UE, rather than the network. The UE informs the network about the selection and communication between the UE and the network proceeds normally. One key difference between femtocell systems and prior art resource allocation methods is that prior art mobile communication networks assume that the network controls all unused resources at a given time. This is a valid assumption when the UE selects a specific cell for the request and the occupied resources are known by the network. However, this assumption is not valid for resource allocation of a femtocell, in that the network does not know which resources are unused at the location of the femtocell when the femtocell makes a resource request. Furthermore, the network will generally not know the exact current position of the femtocell.
Therefore, despite the foregoing variety of different approaches to network resource management, none of these solutions address the additional complexity relating to spectrum allocation that occurs with arbitrary femtocell deployment. In the context of UMTS, the prior art solutions are not usable for HNBs, as HNBs will be operated in a licensed spectrum. Spectrum usage must remain under the control of the operator who owns and operates the licensed spectrum band. Therefore the allocation of spectrum resources to be used by HNBs must be performed in the Core Network and controlled by the operator. Unfortunately, the RF environment at the location of the HNB is unknown by the Core Network. Accordingly, improved methods and apparatus for efficiently assigning spectrum usage are needed.
Such methods and apparatus would ideally provide a simple control scheme for the network operator to manage spectral resources, while also maintaining ease of use and transparent operation for a non-technical user. Such improved methods and apparatus would also aim to find an unused frequency resource at the location of the HNB for transmission with UEs. Advantageously, the network would select the resource to use by the HNB, with the HNB becoming an extension of the network's base station capability.